In a conventional electroplating apparatus, it is customary to bathe an object to be plated (electrically charged as a cathode) in a tank filled with a plating solution (i.e., electrolyte fluid) and metallic bars or metallic nuggets (electrically charged as an anode), supported in a set of baskets made of titanium or of a plastic material and disposed around each side of the object (e.g., a rotogravure printing cylinder).
In an arrangement for plating a rotogravure cylinder, shown in U.S. Pat. No. 4,352,727 issued to Metzger, and incorporated by reference herein, the metallic bars or metallic nuggets are disposed below the surface of the plating solution. Ions move from the metallic bars or metallic nuggets through the plating solution to the surface of the cylinder (preferably rotating) during the plating process (or in the reverse direction in the deplating process). Where plating is done directly from a plating solution, ions move directly from the solution to the surface of the rotating cylinder.
Over time, refinements of this system have facilitated satisfactory control of the plating process to achieve the desirable or necessary degree of consistent plating and uniformity in the plated surface of an object, particularly in the case of a rotogravure cylinder. However, the complete process is comparatively slow, and extra polishing steps are typically necessary after plating in order to produce a desirable uniform surface (e.g., consistent grain structure) on the object. According to the known arrangement, the overall efficiency of the process necessary to produce a suitably uniform plated surface on an object can be adjusted either by reducing the current density, which increases the plating time but reduces the number or duration of additional polishing steps, or by increasing the current density, which reduces the plating time but increases the number or duration of additional polishing steps.
One of the causes of an undesirable plated surface is that in the known arrangement, during operation a metal sludge, formed from metal displaced from the metallic bars, nuggets or anode, tends to accumulate on and about the object during the plating process, forming uneven and undesirable deposits (typically in areas of low current density). These uneven depositions caused by the sludge necessitates an increased number or longer duration of additional polishing steps. The sludge may also build up between the contact surfaces of the baskets or anodes which may affect the efficiency of the plating process. Other surfaces of the electroplating apparatus may also become fouled with sludge and other matter.
Another method of reducing the effects of the sludge is to expose the object and at least portions of the electroplating apparatus to ultrasonic energy throughout at least a portion of the plating process as described in U.S. Pat. No. 5,925,231 issued to Metzger, incorporated by reference herein. Ultrasonic wave energy has been used successfully in surface cleaning applications. The long-known advantages in using ultrasonic energy in electroplating have also been described in such articles as “Ultrasonics in the Plating Industry,” Plating, pp. 141-47 (August 1967), and “Ultrasonics Improves, Shortens and Simplifies Plating Operations,” MPM, pp. 47-49 (March 1962), both of which are incorporated by reference herein. It has been learned that ultrasonic energy may advantageously be employed to improve the quality (e.g., uniformity and consistency of grain structure) of a plating process by providing for uniformity and efficiency of ion movement. In other applications, it has been found that copper can be plated onto a surface in a production system using ultrasonic energy at up to four times the rate ordinarily possible. It has also been found that the use of ultrasonic energy in an electroplating process provides an increase in both the anode and cathode current efficiency, and moreover, the practical benefit of faster plating with less hydrogen embrittlement (e.g., with less oxidation of the hydrogen on the plating and deplating surfaces).
Accordingly, it would be advantageous to have an electroplating apparatus configured to capitalize on the advantages of substantially removing or eliminating material that is vulnerable to chemical attack or dissolution in the plating solution (or adequately protecting any material that cannot be removed), to prevent the buildup of sludge during the plating process, thereby reducing the number or duration of additional polishing steps. It would also be advantageous to have a electroplating apparatus employing an anode that is not vulnerable to chemical attack or dissolution by the plating solution (e.g., a non-dissolvable anode), for example, by substantially employing non-dissolvable materials (or adequately protecting any material that is not non-dissolvable), and thereby reducing or eliminating material that acts as the source of the sludge, so that the build-up of sludge during the plating process will be substantially reduced or eliminated and a more uniform and consistent grain structure on the plated surface of the object will be obtained. It would further be advantageous to have an apparatus configured to combine the advantages of implementing a non-dissolvable anode with the advantages of ultrasonic energy in plating an object (e.g., a rotogravure cylinder) in order to substantially reduce or eliminate the build-up of metal sludge during the plating process and obtain a more uniform and consistent grain structure on the plated surface of the object through a more efficient process.
It would be desirable to provide a method and apparatus providing some or all of these and other advantageous features.